Biennial Geophysical Seminar “Broadband seismic – the next revolution in geophysical exploration” Kristiansand, Norway, 17-19 March 2014 Title: Integrated Reservoir Monitoring of the Ormen Lange field: Time lapse seismic, Time lapse gravity and seafloor deformation monitoring Authors: Annemieke van den Beukel, Meh Jabeen Zainuddin, Philip Riddell, Knut Terje Noraberg (Norske Shell); Neil Hodgson, Marco Naujoks, Marcin Glegola, Maarten Bomers, Shizhuo Liu (Shell Global Solutions) Introduction The Ormen Lange field is located about 100 km off the coast of Norway in the Møre Basin (Fig.1). The reservoir covers an area of approximately 44 by 8 km, at a depth between approximately 2600 and 2913 mMSL. The water depth varies between 700 and 1100 m. The field has been developed by 4 subsea templates; the A-template delivered first gas in 2007, while the fourth C- template delivered first gas at the end of 2012. Primary development drilling is now nearing completion. Figure 1: Ormen Lange overview. The field map contains gravity benchmarks in blue, and geodesy stations (AMTs) in red. The next phase of development at Ormen Lange includes decisions on infill wells, the installation of compression facilities, and enhanced gas recovery. These decisions require a good understanding of the dynamic behavior of the field. Key uncertainties in this respect are fault seal / compartmentalization, and aquifer influx. Compartmentalization The Egga reservoir is deformed by a multi-tiered polygonal fault system. These faults have throws of up to 75m at top reservoir and grew during reservoir deposition. The fault patterns vary significantly, with a north to south reduction in throw values being most important. The main risk for fault seal is through shale (clay) smear. Pressure data from wells drilled after production start up indicates that individual faults can forms baffles of 20 bar. No evidence for compartmentalization has been observed yet. However strong baffling and compartmentalization remains a risk, especially in the northern area, where reservoir quality decreases and fault throw increases (Fig. 2).
Transcript
Biennial Geophysical Seminar
“Broadband seismic – the next revolution in geophysical exploration”
Kristiansand, Norway, 17-19 March 2014
Title: Integrated Reservoir Monitoring of the Ormen Lange field: Time lapse seismic,
Time lapse gravity and seafloor deformation monitoring
Authors: Annemieke van den Beukel, Meh Jabeen Zainuddin, Philip Riddell, Knut Terje
Noraberg (Norske Shell); Neil Hodgson, Marco Naujoks, Marcin Glegola, Maarten Bomers,
Shizhuo Liu (Shell Global Solutions)
Introduction
The Ormen Lange field is located about 100 km off the coast of Norway in the Møre Basin
(Fig.1). The reservoir covers an area of approximately 44 by 8 km, at a depth between approximately
2600 and 2913 mMSL. The water depth varies between 700 and 1100 m. The field has been
developed by 4 subsea templates; the A-template delivered first gas in 2007, while the fourth C-
template delivered first gas at the end of 2012. Primary development drilling is now nearing
completion.
Figure 1: Ormen Lange overview. The field map contains gravity benchmarks in blue, and
geodesy stations (AMTs) in red.
The next phase of development at Ormen Lange includes decisions on infill wells, the installation of
compression facilities, and enhanced gas recovery. These decisions require a good understanding of
the dynamic behavior of the field. Key uncertainties in this respect are fault seal /
compartmentalization, and aquifer influx.
Compartmentalization
The Egga reservoir is deformed by a multi-tiered polygonal fault system. These faults have throws of
up to 75m at top reservoir and grew during reservoir deposition. The fault patterns vary significantly,
with a north to south reduction in throw values being most important.
The main risk for fault seal is through shale (clay) smear. Pressure data from wells drilled after
production start up indicates that individual faults can forms baffles of 20 bar. No evidence for
compartmentalization has been observed yet. However strong baffling and compartmentalization
remains a risk, especially in the northern area, where reservoir quality decreases and fault throw
increases (Fig. 2).
Seabed
Reservoir
CTemplateB &A
TemplatesD Template
Ormen Lange
40 x 12 km spatial extent
400 – 1200m water depth
Biennial Geophysical Seminar
“Broadband seismic – the next revolution in geophysical exploration”
Kristiansand, Norway, 17-19 March 2014
Figure 2: Polygonal faulting of the Egga reservoir. Deterioration in reservoir quality and
increase in fault throw towards the north increases fault baffling potential and risk of
compartmentalization
Aquifer influx
An aquifer has been interpreted to be connected to the southern half of the field. The aquifer strength
is a significant uncertainty, of particular importance to several infill opportunities that have been
identified in the south. Narrowing this uncertainty also has value for overall field management
decisions. The limited production history in this area does not yet reveal any information on the
strength of the aquifer.
Areal monitoring: feasibility studies and field trials
A range of geophysical monitoring methods has been considered to reduce these key uncertainties,
identify and de-risk future infill well targets, and support long term development decisions.
The following list of technologies has been assessed by a combination of feasibility studies and pilot
programs:
Time-lapse seismic
Seafloor geodesy
Time-lapse gravity
Time-lapse EM
Time-lapse seismic is the most mature technology in this set. It has been shown to deliver important
information on contact movements, depletion patterns, and injection patterns. It also has a higher
lateral resolution than any of the other areal monitoring techniques. However, a feasibility study for
Ormen Lange indicated that the water influx signal will likely be very small and nearly impossible to
detect. Furthermore, the strength of the depletion signal is such that it would take a very high quality
survey, and 5+ years of production, to detect this signal. Three complementary non-seismic
technologies were therefore assessed.
The continuous measurement of surface deformation, with the aim to derive information on
production induced compaction, is a well known method for onshore fields. The application of this
technology offshore in the form of seafloor geodesy is new. The advantage of this technology is that
data is collected continuously, and can thereby provide a detailed view of the compaction behavior of
the reservoir. Data collection is also significantly cheaper than time-lapse seismic. To test and develop
40m
North South
Egga
Sub-Egga B7B6
Deterioration in reservoir qualityIncrease in fault throw
Cumulative gas production (Bcm)
200
220
240
260
280
300
320
0 10 20 30 40 50 60
P/Z
[b
ara
]
Cumulative Gas Production [BCM]
Ormen Lange - P/ Z vs cum field production
Shut in pressures @ end of PBU and pressures from PTAA2 PTA
A2 SIP
A3 PTA
A3 SIP
A7 PTA
A7 SIP
A6 PTA
A6 SIP
B2 PTA
B2 SIP
B3 PTA
B3 SIP
A4 PTA
A4 SIP
A5 PTA
A5 SIP
B6 Stethoscope
B6 PTA
B6 SIP
B7 PTA
B7 SIP
5-3 ST2 October 2009
P/ Z seen minimum (160 BCM)
D7 XPT March 2010
P/Z
(ba
ra)
B6, B7
Core production area wells
P/ Z vs. Cumulative gas production
20 bar
Biennial Geophysical Seminar
“Broadband seismic – the next revolution in geophysical exploration”
Kristiansand, Norway, 17-19 March 2014
A
B
D
C
the technology, a 10 sensor trial was installed in 2007 at Ormen Lange. The sensor network collected
data continuously until 2009. The resulting data had an accuracy of 6mm per km in measuring lateral
displacements.
Offshore time-lapse gravity is a relatively new technology. It has been matured and successfully
applied by joint venture partner Statoil to monitor seafloor subsidence and aquifer influx in a number
of Norwegian gas fields. The size of Ormen Lange combined with its relatively shallow depth below
mud line makes it a good candidate for time-lapse gravity. This was confirmed in a detailed feasibility
study. However, water depth and seafloor temperature at Ormen Lange are more extreme than at any
other surveyed field, which results in data acquisition and processing challenges. Time-lapse data
results from a pilot program conducted in 2007 and 2009 proved this technology feasible at Ormen
Lange.
Time-lapse EM is an immature technology, but would have the advantage of being directly sensitive
to saturation changes, without the need for a complex rock physics model, such as in the case of time-
lapse seismic. A feasibility study was done. The result indicated that while the aquifer influx at
Ormen Lange would be visible on time-lapse EM data, it would take 7+ years for the signal to be
measurable. As time-lapse gravity has both a successful track record as well as a higher sensitivity to
water influx at Ormen Lange, time-lapse EM was not selected.
Thus based on two pilot projects and several feasibility studies, three techniques were selected to
provide spatial monitoring data: time-lapse seismic to provide information on depletion patterns and
potentially baffled or isolated fault blocks, at a high resolution; seafloor geodesy to provide
information on the same, but on a continuous basis and relatively cheaply; and time-lapse gravity to
monitor aquifer influx.
Time-lapse seismic
A baseline for 4D seismic was acquired in 2008. The first monitor
survey is planned for 2014. The time-lapse seismic signal is
primarily expected to be a time shift over the reservoir interval,
related to reservoir depletion and compaction. This response is
difficult to predict (Ref Johnston, and papers referenced therein).
The depletion induced velocity increase has been measured on core
plugs, and the results are calibrated against time-lapse seismic
measurements over other Shell operated North Sea fields. This
portfolio of depleting gas fields is relatively small and diverse
however, so the signal strength remains a key uncertainty. A 2D test
to calibrate the signal strength was considered. However the nature
of the overburden at Ormen Lange makes it likely that time-lapse
2D, without the benefits of 3D processing, would be much noisier
than time-lapse 3D. A 2D test may therefore be inconclusive. The
decision on timing of the first full field monitor survey is therefore
driven by a careful assessment of the feasibility study results, and
uncertainties therein; and the value of early monitoring data.
Figure 3: modelled time shift over the reservoir for the 2014 seismic monitor survey
Time-lapse gravity
Time-lapse gravity measures subsurface mass changes and can therefore be used to detect water
influx and to monitor gas production. A full field baseline survey, the first in a non-Statoil operated
field, was acquired in 2012 with excellent data quality. A first full field monitor survey is planned for
2014. During the 2012 survey further measurements were taken at the pilot stations that were
previously surveyed in 2007 and 2009. This has provided us with time-lapse data from two monitor
surveys over a limited area of the field. The results indicate a significant change in the gravity field
over the main production area due to gas offtake, which is in line with the predicted change from
Biennial Geophysical Seminar
“Broadband seismic – the next revolution in geophysical exploration”
Kristiansand, Norway, 17-19 March 2014
reservoir models. The pressure data indicate that the central part of the field has been subsiding by an
average of approximately 2 cm/year since production start up.
Figure 4: Modelled gravity change 2014-2012: the signal is
positive where significant water influx results in an overall
mass increase; the signal is negative where gas offtake results
